The literature relating to the prior art is as follows:    Korean Patent Registration No. 10-0433179;    Korean Patent Registration No. 10-0446560;    PCT International Patent Publication No. WO98/39347;    J. Korean Chem. Soc., 1994, 34, 783-784;    Nucleic Acids Res. 1992, 20, 3325-3332;    Org. Lett. 1999, 1, 1517-1519; and    Tetrahedron: Asymmetry 2002, 13, 2667-2672.
Recently, the L-isomers of natural or modified nucleosides have received attention as antiviral agents. L-thymidine, L-3′-thiacytidine (3TC), L-2′,3′-dideoxycytidine (L-ddC) and the like exhibit remarkably low toxicity and good antiviral effects, compared to D-nucleosides. Also, L-nucleosides exhibit good effects in antisense oligonucleotide therapy. For this reason, many attempts have been made to effectively synthesize L-nucleosides which are not present in nature, and particularly, there have been studies focused on methods capable of economically producing a large amount of L-carbohydrates that are major intermediates of L-nucleosides, particularly 2-deoxy-L-ribose derivatives.
The prior art relating to the preparation of 2-deoxy-L-ribose will now be described.
A method of preparing 2-deoxy-L-ribose through the reduction and inversion reactions of an epoxy ring compound from D-arabinose as a starting material is known [Korean Patent Registration No. 10-0433179]. In this method, the selectivity in the reduction of the epoxy ring compound is problematic, and a lengthy process consisting of 10 steps should be carried out.
A method of preparing 2-deoxy-L-ribose through a six-step process from L-ribose is known [WO 98/39347, Tetrahedron Lett., 1997, 38, 4199-4202]. L-ribose and phenylselenol, used as main raw materials in this method, are expensive, and in addition, this method is not environment-friendly because tributyltin hydride has an unpleasant odor.
A method of preparing 2-deoxy-L-ribose from L-ascorbic acid via the intermediates 4-cyano-1,2-isopropylidene-1,2(S),3(R)-butanetriol and 2-deoxy-L-ribose-1,5-lactone was reported [J. Korean Chem. Soc., 1994, 34, 783-784]. This method has disadvantages in that the preparation process is lengthy, and an expensive material such as diisoamylborane should be used as a reducing agent.
Various methods of preparing 2-deoxy-L-ribose using L-arabinose as a starting material, including a method of reducing the intermediate 2-(methylthio)thiocarbonyl activating functional group with tributyltin hydride, are known [Nucleic Acids Res. 1992, 20, 3325-3332, Org. Lett. 1999, 1, 1517-1519, Tetrahedron: Asymmetry 2002, 13, 2667-2672]. However, these methods are not suitable for the industrial mass production of 2-deoxy-L-ribose, because these methods employ highly toxic or expensive reagents and have low yield. In addition, a method of preparing 2-deoxy-L-ribose from 2-deoxy-D-ribose is known [Korean Patent Registration No. 10-0446560].